Effects of Space Flight on the Histological Characteristics of the Aortic Depressor Nerve in the Adult Rat: Electron Microscopic Analysis

The effects of microgravity on the histological characteristics of the aortic depressor nerve, which is the afferent of the aortic baroreflex arc, were determined in 10 female adult rats. The rats were assigned for nursing neonates in the Space Shuttle Columbia or in the animal facility on the ground (NASA Neurolab, STS-90), and were housed for 16 days under microgravity in space (μg, n=5) or under one force of gravity on Earth (one-g, n=5). In the Schwann cell unit in which the axons of unmyelinated fibers are surrounded by one Schwann cell, the average number of axons per unit in the μg group was 2.1 ± 1.6 (mean ± SD, n=312) and significantly less than that in the one-g group (3.0 ± 2.9, n=397, p